oxygen gases produced by the process that we have just
described. We may estimate the value of a voltameter at a hundred
francs. If the apparatus operates without appreciable wear, the
amortizement should be calculated at a very low figure, say 10 per
cent., which is large. In continuous operation it would produce more
than 1,500 cubic meters of gas a year, say a little less than one
centime per cubic meter. The caustic soda is constantly recuperated
and is never destroyed. The sole product that disappears is the
distilled water. Now one cubic meter of water produces more than 2,000
cubic meters of gas. The expense in water, then, does not amount to a
centime per cubic meter. The great factor of the expense resides in
the electric energy. The cost of surveillance will be minimum and the
general expenses _ad libitum_.

Let us take the case in which the energy has to be borrowed from a
steam engine. Supposing very small losses in the dynamo and piping, we
may count upon a production of one cubic meter of hydrogen and 500
cubic decimeters of oxygen for 10 horse-power taken upon the main
shaft, say an expenditure of 10 kilogrammes of coal or of about 25
centimes--a little more in Paris, and less in coal districts. If,
consequently, we fix the price of the cubic meter of gas at 50
centimes, we shall preserve a sufficient margin. In localities where a
natural motive power is at our disposal, this estimate will have to be
greatly reduced. We may, therefore, expect to see hydrogen and oxygen
take an important place in ordinary usages. From the standpoint alone
of preservation of fuel, that is to say, of potential energy upon the
earth, this new conquest of electricity is very pleasing. Waterfalls
furnish utilizable energy in every locality, and, in the future, will
perhaps console our great-grandchildren for the unsparing waste that
we are making of coal.--_La Nature._

* * * * *

[Continued from SUPPLEMENT, No. 818, page 13066.]

MUSICAL INSTRUMENTS: THEIR CONSTRUCTION AND CAPABILITIES.

By A.J. HIPKINS, F.S.A.

LECTURE II.

I will now invite your attention to the wind instruments, which, in
Handel's time, were chiefly used to double in unison the parts of
stringed instruments. Their modern independent use dates from Haydn;
it was extended and perfected by Mozart, Beethoven, and Weber; and the
extraordinary changes and improvements which have been effected during
the present cen